Control apparatus

ABSTRACT

A secondary control loop or compensation loop for compensating for mechanical errors of an inertial component is shown. The inertial component has a first torquer winding and a second torquer winding with the first torquer winding being used in a rebalance loop in the usual manner. The second torquer winding is driven by pulse circuits in response to logic signals derived from the various inertial components on the same platform. The pulses used to drive the second torquer winding are weighted to compensate for mechanical inaccuracies and errors in the inertial component attached thereto.

United States Patent 1 Dupuis, Jr. 1 Jan. 30, 1973 [54] CONTROLAPPARATUS 7 Primary Examiner-Donald O. Woodiel Attor'ne -Charles J. Unemach Ronald T. Reilin ll ,T y g g [75] Inventor ThomasE Dupu|s,Jr,Da asex and James A. Phillips [73] Assignee: Honeywell, lnc.,Minneapolis,Minn. 221 Filed: April 1,1969 [571 ABSTRACT [211 App. NOJ 811,896 Asecondary control loop or compensation loop for compensating formechanical errors of an inertial r component is shown. The inertialcomponent has a [52] U.S.Cl ..73/l78 R, 33/226 L first torquer windingand a Second torquer winding [51] lIiLCl. ..G0lc 21/18 with the firsttorquer winding being Bed in a [58] held fSearch---33/226 Z; 73/178,504;rebalance loop in the usual manner. The second 74/522 tor uer windin isdriven by ulse circuits in res onse q 8 P P to logic signals derivedfrom the various inertial com- [56] References cued ponents on the sameplatform. The pulses used to UNITED STATES PATENTS drive the secondtorquer winding are weighted to compensate for mechanical inaccuraciesand errors in 3,238,795 I Greenberg et al. X the inertia] componentattached thereto 2,985,023 5/1961 Weissetal ..33/226 UX 4 Claims, 6Drawing Figures n v |o ie f g z 20 2| TOROUER co m... at; e --l-- mm Ywe 24 I v w'f ig T0 c'ouPu'rea moornen AUGmEN-r COMPENSATION LOOPS 2 zei i ACCEER' GYROS- OMETERS 45 P40 FROM 6- SCALE FACTOR X GYRO L 7ADJUSTMENT FROM MISALIGNMENT ALONG THE Y GYRO Y Axis FIG. 3

'42 FROM lmsAueml-mr 2 same; ALONG THE z AXIS s2 5 43 l2 MASS UNBAL- 57FROM x ANCE ALONG ACCELEROMETER 9 711-": SPIN AXIS 54 '44 FROM Y MASSUNBAL- ACCELEROMETER ANCE ALONG THE INPUT'AXIS INVENTOR. THOMAS E.OUPUIS JR.

ATTORNEY CONTROL APPARATUS BACKGROUND OF THE INVENTION In the past therehave been many attempts to improve the accuracy of inertial navigationsystems. The primary direction taken was to improve the mechanicalprecision of the inertial components and theaccuracy of the associatedelectronics. While this approach led to quite precise inertialcomponents, it also greatly increased the cost of such components. Inmany cases there is a need for the accuracy provided by precisioninertial components, but the expense of such inertial components is sohigh that the user cannot afford them. Of course, it was always possibleto produce low-cost inertial components, however, such components weregenerally not accurate enough for the users purpose. Various schemeshave been proposed in the prior art for improving the accuracy ofcomponents which potentially could be used with less precise inertialcomponents, however, many of these schemes relied on such elaboratesystems that the ultimate cost was still too high.

One successful technique for lowering the cost of inertial componentswas to build low-cost inertial components with a second or secondarytorquer winding. The second torquer winding was then used forcompensating for mechanical inaccuracies of the inertial component. Thisapproach is successful only if the cost of the compensation electronicsis also kept low so that the system costs remain low. In general, analogcompensation schemes have been used, however, problems were encountereddue to DC amplifier drift and other sources of error which potentiallycould produce errors greater than those being compensated.

SUMMARY OF THE INVENTION This invention pertains to electronic circuitryfor compensating for mechanical inaccuracies of an inertial component.More particularly, this invention pertains to electronic circuitry whichuses digital or pulse techniques to compensate for inaccuracies orerrors in an inertial component.

In general, a navigation system includes a platform with gyroscopesand/or accelerometers mounted thereon to sense conditions such asangular rate or displacement and/or acceleration in a three-axiscoordinate system. In a strap-down system, for example, threeaccelerometers and three gyroscopes (gyros) may be mounted on aninertial platform to sense acceleration and angular displacement oftheplatform in v the three-axis coordinate system. Each of the inertialcomponents has its input axis oriented in an X, Y, or Z direction. Ifthere is a'mechanical inaccuracy in the orientation of one of thevarious components, that component will provide an output signal whenthere is an input in a direction orthogonal to its input axis at whichtime the component should not be providing an output signal. Since thereis another component sensing the input, its output signal, when properlyscaled, can be used as a correction factor to electrically correct forthe mechanical misalignment of the input axis of the misalignedcomponent.

Similarly, mass unbalance of the gimbal creates torques about the outputaxis which cause inaccuracies. These torques are caused by forces due toacceleration acting on the mass unbalance, and the output signal of theaccelerometers is thus a measure of the torque produced by the unbalanceof the gimbal. Properly scaled output signals from the accelerometerscan be used to compensate for this extraneous torque. Other extraneoustorques or errors may be generated by the flex leads and nonlinearitiesin the inertial component which can be compensated by using properlyscaled output signals from the same inertial component.

A compensation loop constructed in accordance with this inventionincludes one or more pulse circuits which produce properly scaled pulsesin response to the output signals from one or more of the inertialcomponents on the platform. The pulses so generated are applied to thesecond torquer coil of the inertial component to be compensated.

Accordingly, it is an object of this invention to provide novelelectronic compensation apparatus for compensating for mechanicalinaccuracies of inertial components.

It is a further object of this invention to provide a novel compensationapparatus for inertial components which uses pulse or digitaltechniques.

Further objects and advantages of this inventiOn will become evident tothose skilled in the art upon a reading of this specification andappended claims in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of oneexample of a rebalance loop and compensation loop for a gyro.

FIG. 2 is a schematic diagram of a gyro.

FIG. 3 is a block diagram of the pulse circuits in the compensationloop. 1

FIG. 4 is a schematic diagram of a pulse circuit.

FIG. 5 is a schematic diagram to illustrate misalignment of the inputaxis of a gyro.

FIG. 6 is a schematic diagram to illustrate mass unbalance of the gimbalof a gyro.

STRUCTURE OF FIG. 1

In FIG. 1 there is shown an inertial component, inertial instrument, orgyroscope (gyro) 10 for measuring a condition such as angulardisplacement or rate, acceleration or velocity. Gyro 10 has associatedwith it a first force producing means or first or primary torquer coilor winding 1 1; a second force producing means or second, secondary, orauxiliary torquer coil or winding 12; and a signal generator or pickoff13. An output of signal generator 13 is connected to a pre-amplifier 14which has an output connected to a detector 15. An output of detector 15is connected to a logic circuit 16. A strobe or clock 17 has an outputconnected to logic circuit 16. Logic circuit 16 has an output connectedto a switching bridge or circuit 20. A regulated current source 21provides a current to switching bridge 20 which has an output connectedto the first torquer coil 11. Pre-amplifier l4, detector 15, logiccircuit 16, switching bridge 20, aND their associated circuitry comprisea rebalance loop for gyro 10.-

Logic circuit 16 further has first and second logic outputs 22 and 23which are connected to first and second inputs of a compensation andalignment circuit 24. Outputs 22 and 23 of logic circuit 16 are furtherconnected to two terminals for connection to a computer and to thecompensation and alignment loops of other inertial components. Theoutputs of corresponding logic circuits of other inertial components aresimilarly connected to compensation and alignment circuit 24. Theseconnections are illustrated by the connections from accelerometers 18 toinputs 25 and 26 and from gyros 19 to inputs 27 and 28 of compensationand alignment circuit 24. Accelerometers l8 and gyros 19 are the otherinertial components in the system.

A schematic diagram of a integrating rate gyro of a type commonly usedin strap-down systems in shown in FIG. 2. The gyro has a housing 30 witha mounting flange 29 attached thereto. A gimbal 31 is mounted on housing30 and pivoted on bearings 32 and 33. A rotor 34 is mounted inside ofthe gimbal to rotate with the gimbal. The torquer coils 11 and 12 aremounted on one end of the gimbal. The torquer coils may be the same as astandard gyro torquer except that two coils are used instead of one.Pickoff 13 is mounted on the other end of the gimbal. The axis ofrotation of the gimbal is the output axis (A). The axis about which therotor rotates in is the spin axis (SA). The third axis is the input axis(IA) which is mutually perpendicular to the output axis and spin axis.

A integrating rate gyro measures the angular rate about the input axis.The angular rate about the input axis causes the gimbal to precess aboutthe output axis. The precession of gimbal 31 causes pickoff 13 toprovide an output signal. This output signal is amplified bypre-amplifier 14. Detector 15 and logic circuit 16 generate logic pulsesin accordance with the polarity or sense and amplitude of the outputsignal from pre-amplifier 14. The logic pulses from logic circuit 16operate switching bridge 20 to provide pulses of current to torquer coil11. Torquer coil 11 produces a force on gimbal 31 to drive gimbal 31back to its null position. Various pulsing schemes are known in the art.One such scheme is called pulsed-ondemand torquing where logic circuit16 provides pulses to switching bridge 20 when the signal from signalgenerator 13 exceeds a predetermined threshold. The rate of therebalance pulses depends upon the amplitude or rate of change of thesignal from signal generator 13. Logic circuit 16 provides similarpulses at outputs 22 or 23 depending upon the direction of change,polarity, or sense of the signal from signal generator 13.

The gyro illustrated schematically in FIG. 2 is a integrating rate gyrowhich measures angular rate about the input axis. The gyro, however, mayalso integrate so that it in effect measures angular displacement. Sincethe rate or angle of precession of the gimbal is proportional to theangular rate or displacement about the input axis, the output signalprovided by pickoff 13 is proportional to the angular rate or angulardisplacement about the input axis. Since the purpose of the rebalanceloop is to drive the gyro back to null, the rate or' number of currentpulses required to drive the gyro to null is a measure of the angularrate or angular displacement. Logic circuit 16 providesvlogi'c outputsignals at outputs 22 and 23 which are coupled to a computer whichderives navigational information from the logic output signals. Thelogic output-signals provided at outputs 22 and 23 are also'coupled tocompensation and alignment circuit 24. Two outputs are shown in accountfor both plus an minus precession of the gimbal. Other signal schemesmay also be used. These logic signals are used in a manner which will bedescribed hereinafter to pulse torquer coil 12 to provide compensationfor mechanical inaccuracies in inertial component 10.

In a strap-down inertial system, normally three gyros are mounted on theinertial platform. The gyros measure angular rate or displacement aboutthree mutually perpendicular axes. There are also three accelerometerswhich measure acceleration about three mutually perpendicular axes. Eachof these inertial components has a rebalance loop similar to the oneillustrated in FIG. 1. The logic output signals from each of theinertial components can be used to correct or compensate for variousmechanical inaccuracies of each inertial component. The plurality ofinputs 25-28 of compensation and alignment circuit 24 are thereforeconnected to the rebalance loops of the various other inertialcomponents mounted on the same plateform.

STRUCTURES OF FIGS. 3 AND 4 For the description of FIGS. 3 and 4 assumethat inertial component 10 is, the X gyro. Those skilled in the art willrealize that any of the three gyros or three accelerometers in a typicalinertial platform may be compensated in the same manner or in a similarmanner as the X gyro is compensated.

In FIG. 3 blocks 40, 41, 42, 43, and 44 are shown. Block 40, labeledscale factor adjustment, has inputs 45 and 46. Inputs 45 and 46 areconnected to outputs 22 an 23 of logic circuit 16 of FIG. 1. Block 41,labeled misalignment along the Y axis, has inputs 47 and 50. Inputs 47and 50 are connected to outputs of the Y gyro rebalance loopcorresponding to outputs 22 and 23 of logic circuit 16. Block 42,labeled misalignment along the Z axis, has inputs 51 and 52. Inputs 51and 52 are connected to outputs of Z gyro rebalance loop equivalent tooutputs 22 and 23 of logic circuit 16. Block 43, labeled mass unbalancealong the spin axis, has inputs 53 and 54. Inputs53 and 54 are connectedto outputs of the *X accelerometer rebalance loop equivalent to outputs22 and 23 of logic circuit 16. Block 44, labeled mass unbalance alongthe input axis, has inputs 55 and 56. Inputs 55 and 56 are connected tooutputs of the Y accelerometer rebalance loop equivalent to outputs 22and 23 of logic circuit 16. At this point it should be noted that therebalance loops of each of the accelerometers and gyros mounted on theplatform may be the same or similar or may bedifferent. The onlyrequirement is that each of the rebalance loops provide at some point alogic or pulse signal indicative of the condition being sensed by thatinertial component.

Each of the blocks 40-44 has an output connected to one end of torquercoil 12, the other end of which is connected to a common conductor orground 57. All of the outputs of blocks 40-44 can be tied directlytogether since torquer coil 12 is a low impedance load and theinteraction between the outputs of the various blocks will benegligible.

FIG. 4 shows a pulse forming means or pulse circuit suitable for use inblocks 40-44. A first input terminal 60 is connected by means of aparallel combination of a resistor'61 and a capacitor 62 to the base ofa switching means or PNP transistor 63. The collector of transistor 63is connected to one end of a resistor 64, the other end of which isconnected to negative potential source 65. The emitter of transistor 63is connected to one end of a resistor 66, the other end of which isconnected to a positive potential source 67. The emitterof transistor 63is further connected to the cathode of a zener diode 70, the anode ofwhich is connected to ground 57. The collector of transistor 63 isfurther connected to the control means or gate of a switch means,transistor means, or insulated-gate field-effect transistor (FET) 71.The drain of FET 71 is connected to one end of an adjustable means orpotentiometer 7 2, the other end of which is connected to one end of aresistor 73. The other end of resistor 73 is connected to potentialsource 65. The source of transistor 71 is connected to one end oftorquer coil 12, the other end of which is connected to ground 57.Torquer coil 12 is the same in FIGS. 1, 3, and 4. Transistor 63, FET 71,and their associated circuitry comprise a first pulse forming means orpulse circuit.

A second input terminal 74 is connected by means of a parallelcombination of a resistor 75 and a capacitor 76 to the base of a switchmeans or NPN transistor 77. The emitter of transistor 77 is connected toground 57. The collector of transistor 77 is connected to one end of aresistor 80, the other end of which is connected to a positive potentialsource 81. The collector of transistor 77 is further connected to thecontrol means or gate of a switch means, transistor means, orinsulated-gate FET 82. The source of FET 82 is connected to potentialsource 81. The drain of FET 82 is connected to one end of a resistor 83,the other end of which is connected to one end of an adjustable means orpotentiometer 84. The other end of potentiometer 84 is connected to thesource of FET 71 (and hence to one end of torquer coil 12). Transistor77, FET 82, an their associated circuitry comprise a second pulseforming means or pulse circuit.

OPERATION OF FIG. 4

The circuit of FIG. 4 is suitable for use in any of blocks 40-44 of FIG.3. Assume that the circuit of FIG. 4 is being used asblock 40. Inputs 60and 74 are connected to outputs 22 and 23 of logic circuit 16 of FIG. 1.Accordingly, input terminals 60 and 74 correspond to inputs 45 and 46 ofblock 40. When there is no input pulse being provided by logic circuit16, terminals 60 and 74 are both at approximately zero volts. Whenterminal 60 is at zero volts, transistor 63 is conducting so thatcurrent flows from potential source 67 through resistor 66, transistor63, and resistor 64 to potential source 65. The collector of transistor63 will be slightly positive. FET 71 is of a type which will be cut offor non-conducting when its gate-to-source voltage is positive. Since thesource of FET 71 is connected to ground 57 through torque coil 12, FET71 will be non-conduct-' Assume that a positive pulse occurs at inputterminal 60. The positive pulse will cause transistor 63 to become nonconducting or cut off. The collector of transistor 63 will becomenegative so that the gate-tosource voltage of FET 71 will becomenegative. FET 71 will begin conducting. Current will flow from ground 57through torquer coil 12, FET 71, potentiometer 72, and resistor 73 topotential source 65. When the positive pulse at input terminal 60 ends,transistor 63 and FET 71 will return to their initial states orconditions. The magnitude of the pulse of current provided to torquerwinding 12 is regulated by the size of resistor 73 and the setting ofpotentiometer 72.

Assume now that a positive pulse occurs at input terminal 74. Transistor77 will be switched to a conducting state. The potential of thecollector of transistor 77 will drop so that the gate-to-source voltageof FET 82 becomes negative. FET 82 switches to a conducting condition sothat current flows from potential source 81 through FET 82, resistor 83,and potentiometer 84, and torquer coil 12 to ground 57. The magnitude ofthe pulse of current applied to torquer coil 12 is controlled by thesize of resistor 83 and the setting of potentiometer 84. The positivepulse of current applied to torquer coil 12 when FET 82 conducts willnot affect FET 71 because the gate voltage of FET 71 is slightlypositive and the impedance of torquer coil 12 is relatively low.

In summary, when a logic pulse occurs at terminal 74, a positive pulseof current is applied to torquer coil 12. When 'a logic pulse occurs atterminal 60, a negative pulse of current is applied to torquer coil 12.The

size or weight of the pulses of current are controlled by the resistorsand potentiometers in the circuit. Thus, the circuit of FIG. 4 is a dualpulse forming circuit which forms either positive or negative weightedpulses depending upon the direction of the compensation desired.

OPERATION OF FIG. 3

In all inertial components non-linearities, errors or inaccuracies areintroduced due to friction, drag of flex leads, and similar phenomenawhich introduce stray torques. These miscellaneous torques arecompensated by the scale factor adjustment provided by block 40 of FIG.3. These torques are generally of a type which oppose the precession ofthe gimbal. Since the number of pulses required to rebalance the gimbalis a measure of the amount of rotation or movement of the gimbal, thenumber of pulses required to rebalance the gimbal can be used tocompensate for the miscellaneous torques when the rebalance pulses areproperly scaled. Block 40 receives the logic pulses from logic circuit16 of FIG. 1 and provides properly scaled current pulses to torquer coil12. The scaling is provided by adjusting the potentiometers 72 and 84 ofFIG. 4. While potentiometers are shown in FIG. 4, any suitable adjustingmeans may be used and once the proper setting of the potentiometers isdetermined experimentally, the potentiometers may be replaced byresistors of proper sizes. To determine the proper setting ofpotentiometers 72 and 84, the inertial platform may be mounted on aprecision test table and the potentiometers adjusted until the properamount of compensation is provided.

Referring to FIG. 5, there is shown a schematic of gyro housing 30together with arrows indicating the input axis and output axis. A dashedline indicates the direction of the X axis. The X, Y, and Z coordinatesrefer to the platform orientation. When the X gyro is mounted on theplatform, its input axis is generally aligned with the X platformdirection. If the input axis is not exactly aligned with the X axis asindicated in FIG. 5, there is a misalignment of the input axis which iscompensated by the outputs from blocks 41 and 42 of FIG. 3. Themisalignment illustrated in FIG. is greatly exaggerated for illustrativepurposes. The alignment can be corrected mechanically, however, thiscorrection is time consuming and expensive. For the purpose ofexplanation, assume that there is a slight misalignment in the Ydirection and a slight misalignment in the Z direction. When theinertial platform is mounted on a precision test table and there is aninput about the Y axis,,the misalignment of the input axis of the X gyroin the Y direction will cause a small preces sion of the gimbal of the Xgyro. This recession gives rise to an error which is compensated by thecircuit in block 41. Since the logic pulses from theY gyro are a measureof the amount of input about the Y axis, these pulses can be used tocompensate the X gyro for misalignment along the Y axis. The amount ofcompensation needed is determined experimentally with the use of theprecision test table by adjusting the potentiometer in block 41 untilthe X gyro does not provide an output in response to an input about theY axis.

Similarly, block 42 of FIG. 3 is used to compensate for misalignment inthe Z direction by providing properly scaled torque pulses to torquercoil 12 in response to logic pulses from the Z gyro. The procedure fordetermining the scaling is the same as was used for determining thescaling of the logic pulses from the Y gyro. An angular rate input isprovided about the Z axis and the potentiometers in the circuit in block42 are adjusted until there is no output from the X gyro or the outputis within permissible limits.

Referring to FIG. 6, there is shown a schematic of a gimbal lookingalong the output axis. The center of mass of a gimbal must be on theoutput axis for mechanical precision. Assume the center of mass (CM) isslightly displaced from the output axis with components along the spinaxis and input axis. If there is an acceleration in the X direction(along the input axis), there will be a torque about the output axis dueto the mass unbalance along the spin axis. Similarly, if there is anacceleration in the direction of the spin axis, there will be anothertorque about the output axis due to the component of the mass unbalancealong the input axis. Blocks 43 and 44 are used to compensate for thesetorques due to the mass unbalance assuming that the spin axis is alignedwith the Y platform axis.

Since the logic signals from the S accelerometer are a measure of theacceleration in the X direction, these logic signals when properlyscaled can be used to provide compensation for the mass unbalance alongthe spin axis. The amount of compensation required is determinedexperimentally with the use of a precision test table as above. Anacceleration is applied in the X direction and the potentiometers in thepulse circuit in block 43 are adjusted to provide pulses of the properamplitude for compensating for the torque due to the mass unbalancealong the spin axis. Similarly, the pulse circuit in block 44 isadjusted experimentally to compensate for the mass unbalance along theinput axis. The logic pulses from the Y accelerometer are used tocompensate for the mass unbalance along the input axis since the spinaxis is aligned in the Y platform direction. If the spin axis werealigned with the Z platform direction, the logic pulses from the Zaccelerometer would be applied to block 44. Both plus and minus pulsesare used to account for the direction of the acceleration.

From the above description of the compensation loop for the X gyro,anyone skilled in the art can determined how to compensate the Y and Zgyros. As was noted above, a platform ordinarily contains three gyrosand three accelerometers. Those skilled in the art will realize that theaccelerometers can also be compensated for mechanical inaccuracies andnon-linearities with the use of similar apparatus The inaccuracies orerrors to be compensated and the specific circuit construction generallydepend upon the system requirements and the specific application of theinvention is shown and described, those skilled in the art will realizethat many modification can be made within the spirit and scope of theinvention. Accordingly, the scope of the invention is to be limited onlyby the scope of the appended claims.

I claim as my invention:

1. An inertial platform having mounted thereon a plurality of inertialcomponentseach for sensing a particular condition, each having arebalance loop including a primary torquer means and pulse producingmeans for producing pulses indicative of the sense and amplitude of thecondition being sensed, and each further having an auxiliary torquermeans connected to a compensation and alignment means which is connectedto pulse producing means of selected inertial components and producesvariable amplitude current pulses in response to the pulses indicativeof the sense and amplitude of the conditions being sensed by saidselected inertial components and applies the current pulses to theauxiliary torquer, for reducting errors due to mechanical inaccuraciesof said inertial components.

2. A combination as defined in claim 1 wherein said compensation andalignment means for producing variable amplitude current pulses includesa plurality of pulse circuits, each pulse circuit being connected to onepulse producing means and to one auxiliary torquer means.

3. A combination as defined in claim 2 wherein said plurality ofinertial components includes three gyroscopes for sensing angular rateand displacement and three accelerometers, said compensation andalignment means forproducing variable amplitude current pulses includesat least five pulse circuits con nected to the auxiliary torquer meansof each gyroscope with each group of five pulse circuits being connectedto receive pulses from the three gyroscopes and two selected ones of thethree accelerometers.

4. In a navigation system:

a platform;

a first gyro mounted on the platform, having its inputs spring andoutput axes oriented in the X, Y and Z directions, respectively, of a3-axis coordinate system, the gyro including a first and second torquingmeans, the gyro generating a signal which is indicative of a conditionwith respect to its input axis;

logic means for generating first and second sets of pulses in accordancewith the polarity and amplitude of the signal generated by the gyro;

a switching bridge means, including a current source, operated by thefirst set of pulses and providing pulses of current to the firsttorquing means for rebalancing the gyro;

a second gyro means mounted on the platform, having its input axisoriented in the Y direction, and including means for generating a thirdset of pulses in accordance with the polarity and amplitude of a signalwhich is indicative of a condition with respect to the input axis of thesecond gyro means;

a third gyro means mounted on the platform, having is input axisoriented in the Z direction and including means for generating a fourthset of pulses in accordance with the polarity and amplitude of a signalwhich is indicative of a condition with respect to the input axis of thethird gyro means,

first accelerometer means mounted on the platform,

having its input axis oriented in the X direction, and including meansfor generating a fifth set of pulses in accordance with the polarity andamplitude of a signal which is indicative of a condition with respect tothe input axis of the first accelerometer means;

a second accelerometer means mounted on the platform, having its inputaxis oriented in the Y direction, and including means for generating asixth set of pulses in accordance with the polarity and amplitude of asignal which is in indicative of a condition with respect to the inputaxis of the second accelerometer means; and

a compensation and alignment circuit means for applying the second,third, fourth, tifth and sixth sets of pulses in parallel to the secondtorquing means including means for varying the amplitudes of the variousapplied sets of pulses.

UNITED STATES PATENT OFFICE fiERNFEGViE @F (FORECMON 7 Patent No. 3,713, 335 Dated January 30 1973 Inventor(s') Thomas E, Dupuis Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Claim4, line 4, cancelhu'puts spring" and I substitute -pu1:,;spir1,-'-;

' vline 24, cancel is and substitute ---i1:s

line 40, cancel "in" Signed and seeled this 10th day of July 1973.

(SEAL) EDWARD M. FLETCHER,JR. v Rene Tegtmeye-r v Attesting OfficerActing Commissioner of Patents FORM po'wso I I u-scoMM-oc eoa7s-pes QU.S. GOVERNMENT PRINTING OFFXCE I 1969 0-356-334

1. An inertial platform having mounted thereon a plurality of inertialcomponents each for sensing a particular condition, each having arebalance loop including a primary torquer means and pulse producingmeans for producing pulses indicative of the sense and amplitude of thecondition being sensed, and each further having an auxiliary torquermeans connected to a compensation and alignment means which is connectedto pulse producing means of selected inertial components and producesvariable amplitude current pulses in response to the pulses indicativeof the sense and amplitude of the conditions being sensed by saidselected inertial components and applies the current pulses to theauxiliary torquer, for reducting errors due to mechanical inaccuraciesof said inertial components.
 1. An inertial platform having mountedthereon a plurality of inertial components each for sensing a particularcondition, each having a rebalance loop including a primary torquermeans and pulse producing means for producing pulses indicative of thesense and amplitude of the condition being sensed, and each furtherhaving an auxiliary torquer means connected to a compensation andalignment means which is connected to pulse producing means of selectedinertial components and produces variable amplitude current pulses inresponse to the pulses indicative of the sense and amplitude of theconditions being sensed by said selected inertial components and appliesthe current pulses to the auxiliary torquer, for reducting errors due tomechanical inaccuracies of said inertial components.
 2. A combination asdefined in claim 1 wherein said compensation and alignment means forproducing variable amplitude current pulses includes a plurality ofpulse circuits, each pulse circuit being connected to one pulseproducing means and to one auxiliary torquer means.
 3. A combination asdefined in claim 2 wherein said plurality of inertial componentsincludes three gyroscopes for sensing angular rate and displacement andthree accelerometers, said compensation and alignment means forproducing variable amplitude current pulses includes at least five pulsecircuits connected to the auxiliary torquer means of each gyroscope witheach group of five pulse circuits being connected to receive pulses fromthe three gyroscopes and two selected ones of the three accelerometers.